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Author Topic: Adding a second exchanger...  (Read 522 times)

mlappin

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Re: Adding a second exchanger...
« Reply #15 on: January 01, 2019, 06:47:21 PM »

Just spoke with my dealer again about the damper plate issue and he said that after speaking with his rep, they advised that I extend the length of my flue pipe and put a cap on it.  He said that should fix the problem and if it did not they would move forward with sending a new air box.  He said they think it's getting too much down draft. Thoughts??


Itís possible it can help. The way it was explained to me is its strictly an environmental issue. Due to the lay of the land someplace are more prone to temperature inversions which contributes to the damper sticking. I used to see it all the time with my old stove, smoke would go so far up out of the stack then drop and hug the ground down the hill, across the pasture and finally cross the road a 1/4 mile away. In my case installing I guess what would be called the second gen air box fixed it, running for over three moths and havenít cleaned it yet, last year I just planned on weekly with the original box.
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E Yoder

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Re: Adding a second exchanger...
« Reply #16 on: January 05, 2019, 05:08:11 AM »

It is at the same level as the basement, so 25' below the attic.
I'm finishing a job on an old 1860's farmhouse next week with 3 air handlers, the attic unit is at least 30' higher than the top of the outdoor furnace. Am tieing it into one of the basement secondary loops. I think it'll work fine, but it's about the highest I've done. Two stories plus the basement, 12' ceilings. Stove is downhill from the basement.
Homeowner said the original owners started the house in 1860, went off to war, came come home and finished it up. Interesting history.
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greasemonkoid

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Re: Adding a second exchanger...
« Reply #17 on: January 05, 2019, 11:21:25 PM »

Doubt my math is right, but that looks to be approaching the point of needing a restriction on the return side to prevent boiling in the pipe on the way down, but aside from making noise what harm would boiling water on that side do anyway?
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wreckit87

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Re: Adding a second exchanger...
« Reply #18 on: January 06, 2019, 01:38:19 AM »

Doubt my math is right, but that looks to be approaching the point of needing a restriction on the return side to prevent boiling in the pipe on the way down, but aside from making noise what harm would boiling water on that side do anyway?

Genuine curiosity tells me to ask: why would it boil after the reduction in temp from the HX just due to the vertical drop?
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greasemonkoid

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Re: Adding a second exchanger...
« Reply #19 on: January 06, 2019, 08:42:00 AM »

Mainly when the "if's" align, but in reality they probably never will unless you go significantly higher, but that's theory. It would be a neat experiment to try though. The absolute pressure at the crown of the loop is the concern, it doesn't have to be after the heat exchanger. That's several psi pulling down lowering the absolute pressure, certainly wouldn't want a pump up there. The variables are nothing out of the norm - velocity, areas of high turbulent flow, temperature, altitude, ect.
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wreckit87

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Re: Adding a second exchanger...
« Reply #20 on: January 06, 2019, 05:34:13 PM »

Mainly when the "if's" align, but in reality they probably never will unless you go significantly higher, but that's theory. It would be a neat experiment to try though. The absolute pressure at the crown of the loop is the concern, it doesn't have to be after the heat exchanger. That's several psi pulling down lowering the absolute pressure, certainly wouldn't want a pump up there. The variables are nothing out of the norm - velocity, areas of high turbulent flow, temperature, altitude, ect.

I'm no genius, but I don't think that's how this works. We have closed loops, therefore nothing can come down that doesn't go up and pressure throughout the loop remains fairly constant. Friction between the fluid and pipe wall will only allow (X) flow rate which happens to be roughly 3 feet per second on the high side in the majority of residential atmospheric systems. In order for it to flash at 180 degrees, we'd need to see a vacuum of almost 7 psi which would require a water column of 16 feet with a vacuum break on top, which is impossible with a closed loop. I don't see how this could even be accomplished on purpose, much less by accident. Very interesting topic of discussion, but unless there is something I've overlooked it seems to be debunked
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E Yoder

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Re: Adding a second exchanger...
« Reply #21 on: January 07, 2019, 01:36:12 AM »

Here's a thought, stir it around guys. I propose-
 The point of no pressure change is the vent pipe on the outdoor furnace. So, anything above that point is in a slight vacuum. Anything below is under pressure. Both vacuum and pressure would be whatever the water column is, on the job I was describing the attic isabout 30' above the vent pipe, pump serving the attic is about level with the vent pipe.
Anybody be able to figure the temp it could boil? It's about 2000' elevation.
That's why (I feel) it is important to keep pumps as low as possible and at the beginning of any loop they are circulating. This would add the piping resistance in front of the pump to prevent the boiling and cavitation (rather than if the pump were pulling and adding to the vacuum).
I'm guessing that the reason I've never heard boiling in these really high loops is because it's always going through a coil and being cooled.
Thoughts?
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greasemonkoid

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Re: Adding a second exchanger...
« Reply #22 on: January 07, 2019, 04:39:45 AM »

I don't know how to articulate the idea any better. Our closed loop systems are still exposed to atmosphere on both ends, so basically you've got a siphon tube, albeit a modified one, being the presence of a pump creating pressure and velocity of the fluid. We agree that if the pump were to stop, and velocity were to stop, and the loop being high enough, your max siphon height will see a limit.

Now, let's make our hypothetical loop 100' vertical initially filled with water, install an absolute pressure gauge (properly) at the peak of the loop, at the beginning of the upboud side (after the pump), and ending of the down bound side, slowly ramp up pump rpm. What do they read as impeller rpm transitions from 0 rpm to 2000 rpm? What is in the crest of the loop (water or water vapor) and at what rpm?

Sheer forces within the boundary layer (restriction) are on our side this time.
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E Yoder

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Re: Adding a second exchanger...
« Reply #23 on: January 15, 2019, 05:36:59 AM »

This is the coil in the attic we did the other day. Took domestic water pressure to purge out, definitely gettting up there. . I'm guessing 30' above the outdoor furnace.
But it worked fine once the air was out.
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